I think this talk has been presented a couple of times (strata, the meetup), but unfortunately I haven’t seen it yet. Is there a publicly-available recording of it being presented? I have been able to find the slides, but it would be great to watch the actual presentation.
There is a video online from QCon SF last year: http://www.infoq.com/presentations/approximation-algorithms
The meetup talk is different from that one and covers the sketches folks at Yahoo have been working on.